Techniques for integrating a metal and a resin with each other are demanded in a wide variety of fields such as those of manufacturing parts of automobiles, home electrical products, industrial equipment, etc. For this purpose, many adhesives have been developed. Among them are very excellent adhesives. Adhesives that exhibit their function at ordinary temperature or upon heating are used for bonding to integrate a metal and a synthetic resin with each other. The bonding method using such an adhesive is now a common technique.
Meanwhile, researches have heretofore been made to find an even more rational bonding method that does not use an adhesive. However, a method of integrating a high-strength engineering resin with light metals such as magnesium, aluminum and alloys thereof or iron alloys such as stainless steel without using an adhesive has not yet been put to practical use as far as the present inventors know. Examples of such a method include a method wherein a resin component is bonded to a metal by injection or other similar process. This method is named “injection bonding method”.
The present inventors conducted exhaustive studies and development and found that bond strength increases uniquely if a shaped metal material is dipped in an aqueous solution of ammonia, hydrazine, or a water-soluble amine compound and thereafter brought into contact with a thermoplastic resin composition containing polybutylene terephthalate (hereinafter referred to as “PBT”) as a main component under ordinary injection molding temperature and pressure conditions (see WO 03/064150 A1).
It has also heretofore been known that a metal-and-resin composite product is formed by insert-molding a metal product [for example, see Japanese Patent Application Unexamined Publication (KOKAI) Nos. 2001-225352, Sho 54-13588, Sho 54-13587, Sho 58-217679, Sho 50-158539, and Hei 5-70969]. However, these conventional composite producing methods are for producing electric contacts, aluminum foil, etc., and hence unapplicable to mechanical structures that are required to exhibit strong bond strength (adhesion) and rigidity.
The present inventors further carried out researches to investigate whether or not the above-described increase in bond strength would occur with other kinds of resins. In electron microscope observation of an aluminum alloy dip-treated in an aqueous solution of ammonia, hydrazine or a water-soluble amine compound in the above-described invention proposed by the present inventors, it is revealed that fine recesses having a diameter of 30 to 300 nm are present on the aluminum alloy surface. Observation by X-ray photoelectron spectroscopy reveals that a large amount of nitrogen atoms are present on the aluminum alloy surface.
The above-described facts show that the aluminum alloy surface has been etched extremely finely, and nitrogen compounds attributable to ammonia, hydrazine or a water-soluble amine compound are present on the aluminum alloy surface. The present inventors infer that ammonia, hydrazine or a water-soluble amine compound is chemically adsorbed to the aluminum atoms. If an exothermic reaction takes place when the thermoplastic resin composition contacts the chemisorbed substances, the resin composition may enter the fine recesses on the aluminum alloy surface without rapidly cooling to become solidified.
PBT is an aggregate of carboxylic acid esters, and it is known that carboxylic acid esters exothemically react with an amine compound to form a carboxylic acid amide and an alcohol. This shows that our inference is valid. Then, we examined other polymers that may exothermically react with ammonia, hydrazine or an amine compound as in the case of PBT. One of them is polyphenylene sulfide.
This resin is an engineering plastic material developed by Phillips Petroleum Company, U.S.A., which is produced by desalting polycondensation reaction of p-dichlorobenzene, sodium hydrogensulfide and caustic soda. Because of the production method thereof, the polyphenylene sulfide has a composition containing not only high-molecular weight polyphenylene sulfide but also 3 to 10% low-molecular weight oligomers having several or ten-odd or several tens of phenylene groups.
Moreover, many of these oligomers and polymers have chlorine at the molecule end. The present inventors inferred that the chlorine end reacts with amines, which are basic, under high-temperature conditions while generating heat to form salt. Experimental results revealed that polyphenylene sulfide is also capable of injection-bonding to an aluminum alloy treated in the same way as the above. Although further experiments are needed to evaluate the validity of the above-described inference, it will be a good guideline for understanding the present invention in horizontal development.
With the above-described technical background, the present invention was made to attain the following objects.
An object of the present invention is to obtain an aluminum alloy-and-resin composite wherein a thermoplastic resin composition and a shaped aluminum alloy material are made to adhere so strongly that they will not readily separate from each other by treating the aluminum alloy surface, and also obtain a production method therefor.
Another object of the present invention is to obtain an aluminum alloy-and-resin composite capable of making housings and parts of various devices, structures, etc. free from problems in terms of configuration, structure and mechanical strength, and also obtain a production method therefor.
Still another object of the present invention is to obtain an aluminum alloy-and-resin composite useful for reducing the weight of housings and parts of electronic devices, structures, etc. and for simplifying device manufacturing processes, and also obtain a production method therefor.